U.S. patent number 5,949,503 [Application Number 08/668,943] was granted by the patent office on 1999-09-07 for reflective liquid crystal spatial light modulator and projection apparatus comprising same.
This patent grant is currently assigned to Nikon Corporation. Invention is credited to Motoo Koyama, Hideaki Shimomura.
United States Patent |
5,949,503 |
Koyama , et al. |
September 7, 1999 |
Reflective liquid crystal spatial light modulator and projection
apparatus comprising same
Abstract
Reflective spatial light modulators (RSLMs) and projection
apparatus employing such RSLMs are disclosed. The RSLM comprises a
reflective surface and a superposed light-modulation layer. The
reflective surface is configured to have a reflective diffraction
optical element or a microfaceted reflective array. Incident light
impinging on the RSLM can pass through the light-modulation layer,
reflect from the reflective surface, and return through the
light-modulation layer to become modulated signal light capable of
forming a viewable image if projected onto a screen or other
surface. The reflective diffraction optical element or microfaceted
reflective array on the reflective surface is operable to cause the
signal light to propagate from the RSLM in a different direction
than any ghost light reflected from the RSLM. Projection apparatus
employing such an RSLM comprise an illumination optical system, a
projection optical system that may or may not be coaxial with the
illumination optical system, and a stop operable to pass signal
light but not ghost light to a screen for viewing. The viewed image
has enhanced contrast over the prior art.
Inventors: |
Koyama; Motoo (Kawasaki,
JP), Shimomura; Hideaki (Kawasaki, JP) |
Assignee: |
Nikon Corporation (Tokyo,
JP)
|
Family
ID: |
27309561 |
Appl.
No.: |
08/668,943 |
Filed: |
June 24, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Jun 22, 1995 [JP] |
|
|
7-179369 |
Apr 1, 1996 [JP] |
|
|
8-101858 |
Apr 11, 1996 [JP] |
|
|
8-115775 |
|
Current U.S.
Class: |
349/41;
348/E5.141; 349/10; 353/38; 353/37; 349/201; 349/86; 353/97;
353/122 |
Current CPC
Class: |
G02F
1/133553 (20130101); H04N 5/7441 (20130101); G02F
1/1334 (20130101); G02F 2203/22 (20130101); G02F
2201/305 (20130101); G02F 2203/34 (20130101) |
Current International
Class: |
G02F
1/1335 (20060101); H04N 5/74 (20060101); G02F
1/13 (20060101); G02F 1/1334 (20060101); G02F
001/136 () |
Field of
Search: |
;349/201,86,10
;353/37,38,97,122 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Sikes; William L.
Assistant Examiner: Hollingshead; Robert J.
Attorney, Agent or Firm: Klarquist Sparkman Campbell Leigh
& Whinston, LLP
Claims
What is claimed is:
1. A projection apparatus, comprising:
(a) an illumination optical system operable to provide an
illumination light flux;
(b) a reflective spatial light modulator positioned to receive the
illumination light flux, the reflection spatial light modulator
comprising a reflective surface, a light-modulation layer
superposed on the reflective surface, the light-modulation layer
being operable to produce a signal light from incident light
impinging on the reflective spatial light modulator, the signal
light being propagated by the reflective spatial light modulator in
a direction sufficiently different from any ghost light reflected
from the reflective spatial light modulator so as to allow the
ghost light to be blocked relative to the signal light;
(c) a stop defining an aperture, the stop being positioned so as to
allow passage through the aperture of the signal light propagated
by the reflection spatial light modulator, but not the ghost light;
and
(d) a reflective diffraction optical element situated on the
reflective surface of the reflective spatial light modulator,
wherein the reflective diffraction optical element comprises an
array of phase shifters operable to produce higher orders of
diffracted signal light that propagate from the reflective spatial
light modulator in different directions than the ghost light, and
to cancel zeroth-order diffracted light.
2. The projection apparatus of claim 1, wherein the reflective
spatial light modulator further comprises a microfaceted reflective
array on the reflective surface.
3. The projection apparatus of claim 2, wherein the microfaceted
reflective array comprises a regular array of pyramids.
4. The projection apparatus of claim 2, wherein the microfaceted
reflective array comprises a regular array of longitudinal valleys
and ridges.
5. A projection apparatus comprising:
(a) an illumination optical system operable to provide an
illumination light flux;
(b) a reflective spatial light modulator positioned to receive the
illumination light flux, the reflection spatial light modulator
comprising a reflective surface, a light-modulation layer
superposed on the reflective surface, the light-modulation layer
being operable to produce a signal light from incident light
impinging on the reflective spatial light modulator, the signal
light being propagated by the reflective spatial light modulator in
a direction sufficiently different from any ghost light reflected
from the reflective spatial light modulator so as to allow the
ghost light to be blocked relative to the signal light;
(c) a stop defining an aperture, the stop being positioned so as to
allow passage through the aperture of the signal light propagated
by the reflection spatial light modulator, but not the ghost light;
and
(d) a microfaceted reflective array on the reflective surface of
the reflective spatial light modulator, the microfaceted reflective
array comprising a regular array of cones.
6. A reflective spatial light modulator, comprising:
(a) a reflective surface;
(b) a light-modulation layer superposed on the reflective surface,
the light-modulation layer being operable to modulate incident
light passing through the light-modulation layer so as to produce a
signal light;
(c) a transparent layer superposed on the light-modulation layer;
and
(d) a reflective diffraction optical element on the reflective
surface operable to produce higher diffraction orders of signal
light and to substantially cancel zero-order signal light.
7. The reflective spatial light modulator of claim 6, operable to
propagate the higher orders of signal light from the reflective
spatial light modulator in directions that are sufficiently
different from any ghost light reflected from the reflective
spatial light modulator so as to allow the ghost light to be
blocked relative to the higher orders of signal light.
8. The reflective spatial light modulator of claim 6, wherein the
reflective optical element comprises phase shifters situated in a
regular array on the reflective surface.
9. The reflective spatial light modulator of claim 8, wherein each
phase shifter is operable to impart a phase shift of about
.lambda./2 to light of wavelength .lambda. passing through the
phase shifter, reflecting from the reflective surface, and
returning through the phase shifter, compared to light reflecting
from the reflective surface without passing through the phase
shifter.
10. The reflective spatial light modulator of claim 6, wherein the
reflective optical element comprises a regular array of
indentations and protrusions arranged on the reflective surface,
the indentations and protrusions being configured to impart a phase
shift of about .lambda./2 to light of wavelength .lambda.
reflecting from an indentation compared to light of wavelength
.lambda. reflecting from a protrusion.
11. A projection apparatus comprising:
(a) an illumination optical system operable to provide an
illumination light flux;
(b) a projection optical system operable to project a signal light
flux to a viewing surface, the illumination optical system and the
projection optical system being coaxial with each other; and
(c) a reflective spatial light modulator situated relative to the
illumination optical system and the projection optical system so as
to produce the signal light flux from the illumination light flux
impinging on the reflective spatial light modulator and to direct
the signal light flux to the projection optical system, the
reflective spatial light modulator (i) comprising a reflective
surface and a light-modulation layer superposed on the reflective
surface, and (ii) canceling signal light of a specific order by
interference with light of a different phase, while directing the
signal light of another order that is different from that of the
specific order, to the viewing surface.
12. The projection apparatus of claim 11, wherein the
illumination-light flux impinges upon the reflective spatial light
modulator normal to the reflective spatial light modulator.
13. The projection apparatus of claim 11, wherein the reflective
spatial light modulator comprises a reflective diffraction optical
element.
14. The projection apparatus of claim 13, wherein the reflective
diffraction optical element comprises phase shifters arrayed in a
regular pattern on the reflective surface, each phase shifter being
operable to impart a phase shift of about .lambda./2 to light of
wavelength .lambda. passing through the phase shifter, reflecting
from the reflective surface, and returning through the phase
shifter, compared to light reflecting from the reflective surface
without passing through the phase shifter.
15. The projection apparatus of claim 13, wherein the reflective
diffraction optical element comprises a regular array of
indentations and protrusions arranged on the reflective surface,
the indentations and protrusions being configured to impart a phase
shift of about .lambda./2 to light of wavelength .lambda.
reflecting from an indentation compared to light of wavelength
.lambda. reflecting from a protrusion.
16. The projection apparatus of claim 11, wherein the reflective
spatial light modulator comprises a microfaceted reflective array
on the reflective surface.
17. The projection apparatus of claim 11, wherein the projection
optical system comprises, in order from the reflective spatial
light modulator side, a first lens group, an exit-side aperture,
and a second lens group.
18. The projection apparatus of claim 17, wherein the illumination
optical system comprises an illumination-side aperture situated
between the first lens group and the second lens group such that
the illumination-light flux passes through the illumination-side
aperture to be refracted by the first lens group for impingement on
the reflective spatial light modulator.
19. The projection apparatus of claim 18, wherein the exit-side
aperture is situated between the first lens group and the second
lens group such that the signal light flux, but substantially no
ghost light, passes through the exit-side aperture to be refracted
by the second lens group for impingement on the viewing
surface.
20. The projection apparatus of claim 19, wherein the
illumination-side aperture and the exit-side aperture are defined
by a stop disposed between the first and second lens groups.
21. The projection apparatus of claim 20, wherein the stop is
operable to block the ghost light while allowing the signal light
flux to pass through the exit-side aperture to the viewing
surface.
22. The projection apparatus of claim 20, wherein the stop is
operable to pass ghost light back through the illumination-side
aperture rather than the exit-side aperture, thereby preventing the
ghost light from reaching the viewing surface.
Description
FIELD OF THE INVENTION
This invention pertains to reflective spatial light modulators and
projection apparatus that use a reflective spatial light modulator,
and especially pertains to projection apparatus that project light,
that has been modulated by a reflective spatial light modulator,
onto a viewing surface such as a screen.
BACKGROUND OF THE INVENTION
FIG. 1 depicts a prior-art projection apparatus comprising a light
source 1, an illumination lens 2, a stop 3 defining an
incident-side aperture 3a and an exit-side aperture 3b, a front
lens group 4, a reflective spatial light modulator (RSLM) 5 (such
as a "light valve" as known in the art), a rear lens group 6, and a
surface ("screen") 7 on which reflected modulated light from the
RSLM 5 creates a viewable image. The front lens group 4 and the
rear lens group 6 are arranged on an optical axis z and constitute
a "projection optical system" of the apparatus. The light source,
illumination lens, and incident-side aperture comprise an
"illumination optical system" of the apparatus. A parallel
illumination light flux 1a, produced by the light source 1, is
focused by the illumination lens 2 so as to converge at the
incident-side aperture 3a. The front lens group 4 refracts the
illumination light flux 4a diverging from the incident-side
aperture 3a to produce a substantially parallel incident light flux
(rays 4b) that impinge, at an angle to the optical axis z, on the
RSLM 5. The RSLM 5 produces, from the incident light flux, a
reflected modulated light flux (rays 8) that is refracted by the
front lens group 4 to converge at the exit-side aperture 3b. The
rear lens group 6 refracts, and thus projects, the modulated light
flux (rays 6a) diverging from the exit-side aperture 3b to the
screen 7 or analogous viewing surface that forms a viewable image
from the modulated light flux (rays 6b).
A schematic cross section of a representative RSLM 5 according to
the prior art, shown in FIG. 2, comprises a light-modulation layer
5b situated between a reflective surface 5a and a plane-parallel
transparent layer 5c. The reflective surface 5a is substantially
planar in profile and is parallel to the transparent layer 5c. The
transparent layer 5c has a substantially planar surface 5d.
FIG. 3 depicts details of the stop 3 utilized in the apparatus of
FIG. 1. The stop 3 comprises a light-shielding body that defines an
incident-side aperture 3a, through which the illumination light
flux passes to the RSLM 5, and an exit-side aperture 3b through
which the modulated light flux passes to the screen 7. Both
apertures 3a, 3b are arranged symmetrically around the optical axis
z (extending normal to the plane of the page) of the lens groups 4,
6.
Referring further to FIG. 2, the light-modulation layer 5b of the
RSLM 5 is disposed closer than the reflective surface 5a to the
projection optical system 4, 6. Also, the transparent layer 5c,
which can be protective glass or the like, is situated closer to
the projection optical system 4, 6 than the light-modulation layer
5b.
FIG. 1 depicts two categories of light reflected from the RSLM 5.
"Signal" light (rays 8, 6a, 6b denoted by solid lines) represents
light that, after having passed as incident light through the
transparent layer 5c and the light-modulation layer 5b, reflects
from the reflective surface 5a and passes again through the
light-modulation layer 5b and the transparent layer 5a. "Ghost"
light (indicated by dashed lines, e.g., rays 9) represents light
that, as incident light, is reflected from the surface 5d of the
transparent layer 5c without penetrating to the light-modulation
layer 5b or the reflective surface 5a. Since the reflective surface
5a and the transparent layer 5c are planar and parallel to each
other, the signal light 8 and the ghost light 9 are parallel to
each other between the RSLM 5 and the front lens group 4. The front
lens group 4 causes the signal light 8 and the ghost light 9 to
converge at the same point at the exit-side aperture 3b.
Unfortunately, however, because the signal light and ghost light
both pass through the exit-side aperture 3b, both propagate to the
screen 7, where the ghost light diminishes image contrast.
A conventional RSLM 5 that utilizes scattering, such as an RSLM
employing a polymer dispersion-type liquid crystal (PDLC) element
as the light-modulation layer, requires that incident light be at
an angle of incidence significantly greater than zero degrees to
adequately separate "exit" light (i.e., light propagating from the
RSLM) from incident light (i.e., light propagating to the RSLM).
Unfortunately, this can complicate the construction of a projection
apparatus employing the RSLM.
SUMMARY OF THE INVENTION
The foregoing shortcomings of the prior art are solved by the
present invention, which provides, inter alia, an RSLM, comprising
a reflective layer and a light-modulation layer superposed on the
reflective layer, operable to direct reflected modulated "signal
light" in a different direction, relative to the plane of the RSLM,
from reflected ghost light, thereby allowing the ghost light to be
selectively blocked from reaching the screen.
To effect such routing of signal light relative to ghost light, an
RSLM according to the present invention preferably comprises either
a "reflective diffraction optical element" or a "microfaceted
reflective array" situated on the reflective surface.
The reflective diffraction optical element causes diffraction of
modulated light reflecting from the reflective surface. I.e., the
reflective diffraction optical element produces various diffraction
orders of reflected modulated light. Zeroth-order diffracted light
is preferably cancelled by interference and thus does not propagate
from the RSLM. Higher orders of diffracted light propagate from the
RSLM in different directions than the ghost light.
According to a first representative embodiment, the reflective
diffraction optical element comprises an array of phase shifters on
the reflective surface. Each phase shifter preferably imparts a
phase shift of about .lambda./2 to modulated light of wavelength
.lambda. passing through the phase shifter, reflecting from the
reflective surface, and returning through the phase shifter.
According to a second representative embodiment, the reflective
diffraction optical element comprises an array of indentations and
protrusions arranged on the reflective surface. The indentations
and protrusions are preferably configured to impart a phase shift
of about .lambda./2 to modulated light of wavelength .lambda.
reflecting from an indentation compared to light of that wavelength
reflecting from a protrusion.
Various embodiments of a microfaceted reflective array are
possible, including but not necessarily limited to, regular arrays
of convex pyramids, concave pyramids, and combinations of convex
and concave pyramids; convex cones, concave cones, or combinations
of convex and concave cones; and ridges and valleys.
According to another aspect of the present invention, various
projection apparatus are provided that employ an RSLM according to
the present invention. Such projection apparatus exhibit simple
construction and can produce on a screen or other suitable viewing
surface an image, from the RSLM, having excellent contrast without
significant degradation of image quality due to ghost light. The
apparatus comprises a projection optical system and an illumination
optical system. The illumination optical system is operable to
provide an illumination light flux, and the projection optical
system is operable to project signal light from the RSLM to the
viewing surface. The illumination optical system can be either
coaxial or not coaxial with the projection optical system. Whenever
these systems are coaxial, the illumination light flux preferably
impinges normally on the RSLM.
According to a preferred embodiment, the projection optical system
comprises, in order from the RSLM side, a first lens group, an
exit-side aperture, and a second lens group. Also, according to a
preferred embodiment, the illumination optical system comprises an
illumination-side aperture situated between the first lens group
and the second lens group such that illumination-light flux passes
through the illumination-side aperture to be refracted by the first
lens group for impingement on the RSLM. The exit-side aperture is
preferably situated between the first lens group and the second
lens group such that signal-light flux, but substantially no ghost
light, passes from the first lens group through the exit-side
aperture to be refracted by the second lens group for impingement
on a viewing surface ("screen").
Preferably, the illumination-side aperture and the exit-side
aperture are both defined by a stop disposed between the first and
second lens groups. The exit-side aperture can comprise multiple
orifices defined by the stop, depending upon the configuration of
the reflective diffraction optical element or the microfaceted
reflective array. The stop can operate to block propagation of
ghost light therethrough or to allow passage of the ghost light
through the illumination-side aperture, not the exit-side aperture,
thus preventing the ghost light from impinging on the screen.
Thus, projection apparatus according to the present invention
produces an image on the screen that has high contrast and can be
simply and conveniently constructed.
Other features and advantages of the present invention can be
ascertained by reference to the following detailed description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic optical diagram of a prior-art projection
apparatus including a prior-art reflective spatial light modulator
(RSLM).
FIG. 2 is a schematic sectional view of a prior-art RSLM, such as
that used in FIG. 1.
FIG. 3 is a plan view of an aperture stop as used in the prior-art
projection apparatus of FIG. 1.
FIG. 4 is a schematic sectional view of a first example embodiment
of an RSLM, according to the present invention, provided with a
reflective surface having a phase-shifter array.
FIG. 5 is a schematic plan view of the phase-shifter array of the
RSLM of FIG. 4.
FIG. 6 is a schematic sectional view of a second example embodiment
of an RSLM, according to the present invention, provided with an
alternative phase-shifting configuration.
FIG. 7 is a schematic optical diagram of a first representative
embodiment of a projection apparatus according to the present
invention utilizing an RSLM as shown, e.g., in FIG. 4 or 6.
FIG. 8 is a plan view of a stop as employed in the projection
apparatus of FIG. 7, wherein the light axis AX of the projection
optical system extends normal to the plane of the page.
FIG. 9 is a schematic optical diagram of a second representative
embodiment of a projection apparatus according to the present
invention utilizing an RSLM as shown, e.g., in FIG. 4 or FIG.
6.
FIG. 10 is a plan view of a stop as employed in the projection
apparatus of FIG. 9, wherein the light axis AX of the projection
optical system extends normal to the plane of the page.
FIG. 11 is a schematic optical diagram showing general features of
various embodiments of a projection apparatus according to the
present invention utilizing an RSLM provided with a reflective
surface having a microfaceted reflective array, wherein the
projection apparatus comprises an illumination optical system and a
projection optical system that are not coaxial. FIG. 11 also shows
specific aspects of such a projection apparatus employing the RSLM
of FIG. 12.
FIG. 12 is a schematic plan view of the reflective surface of an
RSLM according to the present invention that can be employed in the
FIG. 11 or FIG. 15 embodiment of a projection apparatus, the RSLM
having a first example embodiment of a microfaceted reflective
array on the reflective surface of the RSLM.
FIG. 13 is a schematic depiction of section A--A of FIG. 12.
FIG. 14 is a plan view of the stop employed in the FIG. 11
embodiment of a projection apparatus that includes the RSLM of FIG.
12.
FIG. 15 is a schematic optical diagram showing general features of
various embodiments of a projection apparatus according to the
present invention utilizing an RSLM provided with a reflective
surface having a microfaceted reflective array, wherein the
projection apparatus comprises an illumination optical system and a
projection optical system that are coaxial.
FIG. 16 is a plan view of the stop employed in the FIG. 15
embodiment of a projection apparatus that includes the RSLM of FIG.
12.
FIG. 17 is a schematic plan view of the reflective surface of an
RSLM according to the present invention that can be employed in the
FIG. 11 or FIG. 15 embodiment of a projection apparatus, the RSLM
having a second example embodiment of a microfaceted reflective
array on the reflective surface of the RSLM.
FIG. 18 is a schematic plan view of the reflective surface of an
RSLM that can be employed in the FIG. 11 or FIG. 15 embodiment of a
projection apparatus, the RSLM having a third example embodiment of
a microfaceted reflective array on the reflective surface of the
RSLM.
FIG. 19A is a plan view of the stop employed in the FIG. 11
embodiment of a projection apparatus that includes the RSLM of FIG.
18.
FIG. 19B is a plan view of the stop employed in the FIG. 15
embodiment of a projection apparatus that includes the RSLM of FIG.
18.
FIG. 20 is a schematic plan view of the reflective surface of an
RSLM according to the present invention that can be employed in the
FIG. 11 or FIG. 15 embodiment of a projection apparatus, the RSLM
having a fourth example embodiment of a microfaceted reflective
array on the reflective surface of the RSLM.
FIG. 21A is a plan view of the stop employed in the FIG. 11
embodiment of a projection apparatus that includes the RSLM of FIG.
20.
FIG. 21B is a plan view of the stop employed in the FIG. 15
embodiment of a projection apparatus that includes the RSLM of FIG.
20.
FIG. 22 is a schematic plan view of the reflective surface of an
RSLM according to the present invention that can be employed in the
FIG. 11 or FIG. 15 embodiment of a projection apparatus, the RSLM
having a fifth example embodiment of a microfaceted reflective
array on the reflective surface of the RSLM.
FIG. 23A is a plan view of the stop employed in the FIG. 11
embodiment of a projection apparatus that includes the RSLM of FIG.
22.
FIG. 23B is a plan view of the stop employed in the FIG. 15
embodiment of a projection apparatus that includes the RSLM of FIG.
22.
FIG. 24 is a schematic plan view of the reflective surface of an
RSLM according to the present invention that can be employed in the
FIG. 11 or FIG. 15 embodiment of a projection apparatus, the RSLM
having a sixth example embodiment of a microfaceted reflective
array on the reflective surface of the RSLM.
FIG. 25A is a plan view of the stop employed in the FIG. 11
embodiment of a projection apparatus that includes the RSLM of FIG.
24.
FIG. 25B is a plan view of the stop employed in the FIG. 15
embodiment of a projection apparatus that includes the RSLM of FIG.
24.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A reflective spatial light modulator (RSLM) according to the
present invention typically comprises a modulation layer, a
reflective surface, and a transparent layer. The RSLM is operable
to produce, from incident light, a reflected modulated "signal
light" flux that can be delivered, for example, to a projection
apparatus operable to form a viewable image from the signal light
on a screen or other suitable viewing surface. Notably, the RSLM is
operable to direct the signal light in a direction that is
different from any "ghost light" produced by reflection of incident
light from the RSLM, thereby allowing the ghost light to be blocked
and thus prevented from reaching the signal-light image on the
screen.
As used herein, "signal light" produced by a RSLM is light that
has, after entering the RSLM as incident light, passes through the
light-modulation layer, reflects from the reflective surface, and
passes again through the light-modulation layer. Modulation encodes
information in the light that enables the signal light to produce a
viewable image when the signal light impinges on a screen or other
suitable surface.
As stated above, a notable aspect of an RSLM according to the
present invention is the ability of the RSLM to direct signal light
in a direction that is different from any "ghost light" produced by
reflection of incident light from the RSLM. RSLMs according to the
present invention comprise any of various features that confer such
ability. One feature is termed a "reflective diffraction optical
element" as described in detail below. An alternative feature
providing such ability is a "microfaceted" reflective array, as
also described in detail herein, having any of various
geometries.
Turning first to RSLMs according to the present invention having a
reflective diffraction optical element, a first example embodiment
15 of such an RSLM is depicted schematically in cross section in
FIG. 4. The RSLM 15 comprises a reflective surface 15a, a
light-modulation layer 15b superposed on the reflective surface
15a, and a transparent layer 15c superposed on the light-modulation
layer 15b. The transparent layer 15c has a planar surface 15d that
can be regarded, for reference purposes, as a plane "defined" by
the RSLM. Situated on the reflective surface 15a is a regular array
of phase shifters PS. The array is preferably a checkerboard
pattern as schematically depicted in FIG. 5, wherein the entire
array comprises a "reflective diffraction optical element" 16. In
FIG. 5, the area delineated by the dashed line A corresponds to one
picture element (i.e., one pixel). The area of and spacing between
each phase shifter PS is sufficient to cause substantial
diffraction of incident light as the light reflects from the
reflective diffraction optical element 16.
The thickness dimension of each phase shifter PS is preferably
sufficient to impart a phase difference of approximately 1/4
wavelength to incident light when such light passes once through
the thickness dimension. Thus, incident light of wavelength
.lambda. passing through the thickness dimension of a phase shifter
PS, then reflecting from the reflective surface 15a, and then
returning through the thickness dimension of the phase shifter PS
undergoes a shift in phase of about .lambda./2 compared to light
reflected from the reflective surface 15a without passing at all
through a phase shifter PS.
The RSLM 15, due to the presence of the reflective diffraction
optical element 16, is operable to produce, upon impingement
thereon of incident light (ray 17), various diffraction orders
(e.g., rays 18a, 18b, 18c) of reflected light. In FIG. 4, ghost
light (ray 19) reflects from the surface 15d at an angle of
reflection equal to the angle of incidence. Since some of the 0th
(zeroth) order (ray 18a) of reflected modulated signal light is
phase inverted (i.e., by 180.degree.) by action of the phase
shifters PS and some is not, a destructive interference involving
the 0th-order light results in substantial elimination of all the
0th-order light. I.e., modulated light reflected from portions of
the reflective surface 15a lacking a superposed phase shifter PS
(i.e., reflected modulated light that is not phase shifted)
interferes with modulated light reflected from portions of the
reflective surface 15c having a superposed phase shifter PS (i.e.,
light that has been phase shifted by 180.degree.). However,
first-order and higher-order diffracted light, modulated by the
RSLM, are not cancelled but rather allowed to propagate as
modulated "signal" light.
Referring further to FIG. 4, the light-modulation layer 15b is
preferably formed of a polymer dispersion-type liquid crystal
layered on the reflective surface 15a, thereby sandwiching the
multiple phase shifters PS between the reflective surface 15a and
the light-modulation layer 15b. The transparent layer 15c is
preferably glass. Although not shown in FIG. 4, the RSLM can also
include any of various other functional films such as (but not
limited to) a photoconductive layer, a transparent conductor (ITO)
film, a light-shield layer, or an anti-reflective film as necessary
or desired. As incident or reflected light passes through the
light-modulation layer 15b, the light is modulated with video
information according to video signals inputted into the
light-modulation layer 15b.
The phase shifters PS can be made of any of various materials
having a different refractive index from the light-modulation layer
15b, and with which absorption is not a problem at the wavelength
being used. For example, the light-modulation layer can be a PDLC
(polymer diffusion liquid crystal) in which the main polymer
ingredient is an epoxy resin. The refractive index n.sub.1 (d-line)
of PDLC is approximately 1.524. With such a light-modulation layer
used with light in the visible spectrum, a silicon nitride, for
example, (in which the main ingredient is Si.sub.3 N.sub.4) having
a refractive index of around 2 can be used as the material for the
phase shifters. The refractive index n.sub.2 of the silicon nitride
can be set within a range of approximately 1.8 to 2.0 by means of
process control.
The refractive indices n.sub.1 and n.sub.2 and the thickness d of a
.lambda./4 phase shifter have the following quantitative
relationship:
wherein N is an integer greater than zero (when n.sub.1
<n.sub.2), and .lambda. is the wavelength of light being used.
Thus, the thickness d of a .lambda./4 phase shifter is expressed by
equation (2), below:
A second example embodiment 25 of an RSLM according to the present
invention having a reflective diffraction optical element is shown
in FIG. 6. The RSLM 25 is provided with an alternative
phase-shifting configuration and is depicted schematically in FIG.
6 in cross section. The FIG. 6 embodiment is structured similarly
to the FIG. 4 embodiment in that the FIG. 6 embodiment comprises a
reflective surface 25a, a light-modulation layer 25b, a transparent
layer 25c, and a planar surface 25d. Instead of using discrete
phase shifters as utilized in the FIG. 4 embodiment, the RSLM 25 of
FIG. 6 utilizes a regular array (e.g., in a checkerboard pattern)
of protrusions 25aT and indentations 25aB on the reflective surface
25a that effect phase shifting.
Further with respect to FIG. 6, the indentations 25aB and
protrusions 25aT collectively comprise a reflective diffraction
optical element. Incident light can reflect from the indentations
25aB and from the protrusions 25aT; however, with a wavelength
.lambda. of incident light, the difference between the phase of
modulated light reflected by an indentation 25aB and the phase of
modulated light reflected by a protrusion 25aT is approximately
.lambda./2.
The size of the protrusions 25aT and indentations 25aB is
appropriate to cause substantial diffraction of light reflecting
therefrom. As in the FIG. 4 embodiment, 0th-order light is
effectively "cancelled" and thus eliminated.
Even though the phase shifters PS in the FIG. 4 embodiment and the
indentations 25aB and protrusions 25aT in the FIG. 6 embodiment are
shown having a square shape, the phase shifters PS, indentations
25aB, and protrusions 25aT are not limited to a square shape.
Furthermore, the phase shifters PS or indentations 25aB and
protrusions 25aT are not necessarily arrayed in a checkerboard
pattern; as long as they are regularly arranged on the reflective
surface with some periodicity, a reflective diffraction optical
element is formed thereby that effectively cancels 0th-order
reflected modulated light.
It is noted that binary optics comprising phase shifters or
indentations and protrusions with multi-stage thicknesses can be
used instead of the phase shifters PS used in the FIG. 4 embodiment
or the indentations 25aB and protrusions 25aT used in the FIG. 6
embodiment. Making such a substitution can result in a specific
higher (non-zero) order of diffracted light being intensified
relative to other higher orders, making it possible to further
improve the efficiency of the use of that light. It is also
possible to further improve use efficiency of the light by having
the format of the multi-stage binary optics be a continuous format
rather than a multi-stage, i.e., non-continuous, format.
The phase shifters PS of the FIG. 4 embodiment and the undulating
structure of the reflective surface 25a of the FIG. 6 embodiment
can be manufactured by, e.g., a photolithographic method, or other
suitable method.
FIG. 7 schematically depicts a first representative embodiment of a
projection apparatus according to the present invention employing,
for example, the FIG. 4 embodiment of an RSLM, or alternatively the
FIG. 6 embodiment of an RSLM. In FIG. 7, a light source 31 provides
a nearly parallel illumination light flux (rays 31B). The light
source 31 is preferably a reflector type that is arranged on a
light axis 31A on which an illumination lens 32 is situated. The
illumination lens 32 converges the illumination light flux, which
reflects from a prism 38, to form a light-source image. An
illumination-light aperture 33A is defined by a stop 33 situated
where the light-source image is formed. As seen in FIG. 8, the
illumination light aperture 33A is defined, preferably as a
circular orifice, by a planar light-shielding body 33C. A first
lens group 34 refracts light from the light-source image,
downstream of the illumination-light aperture 33A, into a parallel
illumination light flux (rays 34A) for impingement on an RSLM 35
(according to, for example, FIG. 4 or FIG. 6). The RSLM 35 is
situated on a light axis AX of the projection optical system.
In FIG. 7, the light source 31, illumination lens 32, prism 38, and
illumination-light aperture 33A comprise an "illumination optical
system" of the apparatus that operates to provide illumination
light to the RSLM 35.
Further with respect to FIG. 7, the light-modulation layer 35b of
the RSLM 35 is driven using a video data input 39a and a controller
39b collectively comprising electronic circuitry, generally as
known in the art, operable to provide video image information
sufficient to cause the RSLM to produce a modulated signal
light.
The video data input 39a can be operable to read video image
information provided from a source (not shown) such as, for
example, a magnetic recording medium (e.g., floppy disk or video
tape), an optical recording medium (e.g., photo CD or MO
(optical-magnetic recording medium)), or electrical recording
medium (e.g., IC card). The video data input 39a can be constructed
as a separate unit from the projection optical apparatus and
electrically connected thereto by an appropriate cable or other
electrical connection means.
As mentioned above, the RSLM 35 comprises a reflective diffraction
optical element as shown, for example, in either FIG. 4 or FIG. 6.
The RSLM can also include a so-called optical write format device
(not shown), wherein video-image information that is input to the
RSLM is displayed on a video-display means, e.g., a CRT or LCD.
Light from the video image displayed on such a video-display means
is directed to the RSLM which performs modulation of incident
light.
Continuing further with FIG. 7, higher orders of modulated
diffracted signal light (rays 34B, 34C) from the RSLM 35 are
focused by the first lens group 34 to form one or more images.
Exit-side apertures 33B are situated at this image-formation
position. Signal light passing through the exit-side apertures 33B
is refracted by a second lens group 36 for projection onto a screen
37 situated on the light axis AX. Thus, a light/dark pattern
corresponding to the light-modulation action of the RSLM 35 based
on the video information input to the RSLM 35 is formed as a video
image on the screen 37.
Ghost light (rays 34D) reflected from the planar surface 35d
propagates from the RSLM 35 in a direction that is different from
that of the signal light. Thus, the ghost light can be effectively
blocked by the stop 33 and does not propagate to the second lens
group 36.
Referring to FIG. 8, the exit-side apertures 33B preferably
comprise multiple orifices 33D (four are shown) defined by an
opaque planar light-shielding body 33C symmetrically about a point
P. The point P is the convergence point for the ghost light (rays
34D).
As discussed above with regard to a prior-art projection apparatus
as depicted, for example, in FIG. 1 and that uses a conventional
RSLM, the modulated signal light and the ghost light reach the
aperture stop along paths that are nearly the same. As a result,
the ghost light propagates together with the signal light to the
screen where the ghost light causes deterioration of image
contrast.
With the projection apparatus of FIG. 7, in contrast, the signal
light is modulated higher-order diffracted light produced by the
reflective diffraction optical element in the RSLM and propagated
in directions different from the direction of propagation of ghost
light. Consequently, the signal light can pass through the
exit-side apertures 33B to the screen, but the ghost light is
blocked at P and thus prevented from propagating to the screen.
In view of the propagation direction of higher-order diffracted
signal light from the RSLM of, e.g., FIG. 4 or FIG. 6, relative to
ghost light, the RSLM can be employed in a projection apparatus in
which the light source is situated coaxially with the projection
apparatus. Such a configuration desirably simplifies the
construction of the projection apparatus, and simplifies any
adjustments of optical components of the projection apparatus that
may be required.
Such a "coaxial" embodiment of a projection apparatus according to
the present invention is depicted in FIG. 9, in which components
that are substantially the same as in FIG. 7 have the same
reference designators. The RSLM 35 can be, e.g., as depicted in
FIG. 4 or FIG. 6. The apparatus of FIG. 9 includes a stop 43
defining an illumination-light aperture 43A and exit-side apertures
43B as detailed in FIG. 9, viewed along the optical axis AX.
The apparatus of FIG. 9, in contrast to that of FIG. 7 in which the
overall structure is asymmetric around the light axis AX (i.e., the
illumination optical system and the projection optical system are
not coaxial), has an overall structure that is symmetric around the
light axis AX (i.e., the illumination optical system and the
projection optical system are coaxial). Although not shown in FIG.
9, it will be understood that, as in FIG. 7, an input 39a and a
controller 39b are preferably used to operate the RSLM 35.
Continuing further with FIG. 9, a parallel light flux (rays 31B)
from the light source 31 (which is situated on the light axis AX)
is converged by the illumination lens 32 (similarly situated on the
light axis AX) to form an image of the light source. An
illumination-light aperture 43A is situated at the position on the
light axis AX at which the light-source image is formed. In FIG. 9,
the light source 31, the illumination lens 32, and the
illumination-light aperture 43A together comprise the "illumination
optical system" of the apparatus. The first lens group 34 and the
second lens group 36 together comprise the "projection optical
system" of the apparatus.
The light passing through the illumination-light aperture 43A is
refracted into a parallel light flux (rays 34A) by the first lens
group 34. The parallel light flux illuminates the RSLM 35, which is
also situated on the light axis AX.
Higher orders of modulated diffracted light (rays 34B, 34C) from
the RSLM 35 are refracted by the first lens group 34 to converge at
the exit-side apertures 43B and propagate therethrough to the
second lens group 36 for projection onto the screen 37 (also
situated on the light axis AX).
FIG. 10, detailing the stop 43, shows that the illumination-light
aperture 43A is coaxial with the light axis AX, whereas the
exit-side apertures 43B comprise multiple orifices 43D arranged
equidistantly from each other symmetrically around the light axis
AX.
Referring further to FIG. 9, modulated diffracted signal light
passes through the orifices 43D and is projected onto the screen 37
by the second lens group 36. Ghost light reflected from the planar
surface 35d of the RSLM 35 returns to the light source 31 via the
illumination-light aperture 43A, and thus does not reach the screen
37. As a result, an image of excellent contrast is obtained on the
screen 37.
Since the illumination optical system of FIG. 9 is coaxial with the
projection optical system, the construction of the overall
apparatus is simplified, and mounting and adjustment of the various
optical components of these systems are simplified.
The number, shape, and arrangement of the orifices 43D and the
illumination-light aperture 43A shown in FIG. 10 (and of
corresponding features shown in FIG. 8) are provided as examples
only. The manner in which to appropriately modify these features
depends upon the pattern of modulated diffracted signal light from
the RSLM 35.
It will be understood that the light paths shown in FIG. 9 may be
bent by a prism or mirror without destroying the overall coaxiality
of the apparatus. For example, a prism can be placed in the light
path between the light source 31 and the illumination-light
aperture 43A so as to direct the illumination-light flux from a
direction intersecting the axis AX into the illumination-light
aperture 43A.
Furthermore, when a projection apparatus according to the present
invention utilizing an RSLM as shown, e.g., in FIG. 4 or FIG. 6, is
employed for full-color projection, a separate RSLM will generally
be used for each of red (R), green (G), and blue (B) light. In such
a case, the patterns of diffracted signal light that form at the
pupil (i.e., at the exit-side apertures 43B) of the first lens
group will differ slightly for each basic color (R, G, and B) of
light. Hence, the light of each basic color that passes through the
exit-side aperture 43B can be controlled relative to the light of
the other basic colors by appropriately selecting the shape and
arrangement of the various orifices of the exit-side aperture 43B.
For example, it is possible to adjust the color balance and control
color purity, etc., of the image on the screen in such a
manner.
Notwithstanding the embodiments shown, for example, in FIGS. 7 and
9 in which the light source 31 supplies a nearly parallel
illumination light, projection apparatus according to the present
invention are not so limited. The light source can supply, e.g.,
divergent light by an appropriate modification of its optically
conjugate relationship with the screen.
In addition, although the embodiments of FIGS. 7 and 9 employ a
reflector-type light source, any other suitable type of light
source may be used.
Another general type of RSLM in accordance with the present
invention that can direct signal light in a different direction
than ghost light has a light-modulation layer superposed on a
reflective surface provided with a "microfaceted" reflective array.
The microfaceted reflective array is an ordered regular array of
multiple tiny reflective facets that individually are not parallel
to the plane of the RSLM. As a result, ghost light and signal light
from such an RSLM converge at different locations, making it
possible to pass only signal light through an exit-side aperture(s)
while blocking ghost light. With such RSLMs, even though incident
light can enter the RSLM perpendicularly (I.e., normal) to the
plane of the RSLM, the signal light exits the RSLM at an angle to
the normal. This allows, with a projection apparatus employing such
an RSLM, the illumination optical system and the projection optical
system of the apparatus to be coaxial. Example embodiments of such
RSLMs are discussed below.
FIG. 11 shows a third representative embodiment of a projection
apparatus according to this invention. The FIG. 11 embodiment
utilizes an RSLM 55 provided with a microfaceted reflective array.
A parallel incident light flux 51B generated by a light source 51
is converged by an illumination lens 52 and an illumination prism
58 at a location on an illumination axis 51A corresponding to the
incident-side aperture 53a. Light that has passed through the
incident-side aperture 53a is refracted into a parallel incident
light flux (rays 54A) by a front lens 54 for impingement on the
RSLM 55. Light that has been modulated by the RSLM 55 (rays 54B,
54C) is converged by the front lens 54 at locations corresponding
to the exit-side apertures 53b, and is projected by the rear lens
56 onto the screen 57. Ghost light (rays 54D) reflected from the
surface 55d propagates in a different direction from the signal
light and is effectively blocked at the point x on the stop 53.
The RSLM 55, detailed in FIG. 12 and FIG. 13, comprises a
light-modulation layer 55b made from polymer dispersion-type liquid
crystal, a reflective surface 55a, and a plane-parallel glass layer
55c with a planar surface 55d. Any of various additional functional
films (not shown), such as a photoconductive layer, a transparent
conductor (ITO) film, a light-shield layer, or an anti-reflective
film can also be included as necessary or desired.
The reflective surface 55a comprises a "microfaceted reflective
array." In the embodiment shown in FIG. 12, the microfaceted
reflective array comprises a regular array of multiple tiny
four-sided pyramids of low elevation. The sides (facets) B of each
pyramid are arranged symmetrically around an apex T. As can be
readily understood from FIGS. 12 and 13, the plane represented by a
facet B is not parallel to the surface 55d (wherein the surface 55d
is parallel to the "plane" of the RSLM).
As shown in FIG. 14, the stop 53 defines one incident-side aperture
53a and usually plural exit-side apertures 53b (preferably four
exit-side apertures when the RSLM used with the apparatus is as
shown in FIGS. 12-13). The exit-side apertures 53b are situated so
as to pass modulated light reflected from the facets B on the
reflective surface 55a. The location x, around which the exit-side
apertures 53b are symmetrically arranged, is where ghost light is
blocked. The location z is where the optical axis Z passes through
the stop 53.
The ghost light that converges at x is reflected by the planar
surface 55d of the transparent layer 55c and/or the planar
interface 55e (parallel to the surface 55d) between the transparent
layer 55c and the light-modulation layer 55b. As shown in FIG. 14,
the location x and the incident-side aperture 53a are symmetrically
arranged relative to the optical axis Z. Signal light, reflected
from the facets on the reflective surface 55a, has passed at least
twice through the light-modulation layer 55b, and thus has been
modulated by the state of the liquid-crystal material comprising
the layer 55b. Because the plane of any facet B is not parallel to
the surface 55d or interface 55e, signal light propagates in
directions that are different from the propagation direction of
ghost light. Thus, signal light converges at the exit-side
apertures 53b and passes therethrough to form a high-contrast image
on the screen 57, while ghost light is blocked by the stop 53 at
location x.
A fourth representative embodiment of a projection apparatus
according to the present invention is shown in FIG. 15 which can
utilize an RSLM having a microfaceted reflective array (such as
shown in FIGS. 12-13). In contrast to the FIG. 11 embodiment (which
is asymmetric about the optical axis z), the FIG. 15 embodiment has
a structure that is symmetric around the light axis Z (i.e.; the
illumination optical system of the FIG. 15 apparatus is coaxial
with the projection optical system). Further with respect to the
FIG. 15 embodiment, the stop 63 (detailed in FIG. 16), defines an
incident-side aperture 63a situated on the light axis Z and usually
plural (preferably four whenever the RSLM is as shown in FIGS.
12-13) exit-side apertures 63b situated equidistantly apart from
one another symmetrically about the axis z. Since ghost light
reflected by the planar surface 55d of the RSLM 55 returns again to
the light source 51, the ghost light is effectively blocked from
the screen 57.
In prior-art RSLMs exploiting scattering, separating scattered
light from direct light (signal light) required that incident light
impinge the RSLM at an angle to the normal of the plane of the RSLM
(e.g., the plane represented by the planar surface of the
transparent layer). In an RSLM according to the present invention
as shown in FIG. 12, in contrast, a normal to any facet B is not
parallel to the normal of the plane of the RSLM. It is thus
possible with the RSLM of FIG. 12 for incident light to impinge the
RSLM normal to the plane of the RSLM while signal light propagates
in a non-normal direction.
Even though the reflective surface 55a of the specific RSLM shown
in FIGS. 12-13 comprises multiple convex four-sided pyramids, the
surface 55a can also comprise multiple concave four-sided pyramids,
or an alternating pattern of convex and concave four-sided pyramids
(e.g., in a checkerboard pattern), as shown in FIG. 17. In FIG. 17,
T denotes the convex apex of a representative convex pyramid and B
denotes the concave apex of a representative concave pyramid.
FIG. 18 depicts yet another example embodiment of an RSLM according
to the present invention, in which the reflective surface 75a
comprises a regular array of multiple six-sided pyramids
collectively comprising a microfaceted reflective array. Each
pyramid has an apex T of low elevation, and six facets B
symmetrically surrounding each apex T. The pyramids can be convex
or concave.
The FIG. 18 embodiment of an RSLM can be employed in any of various
projection apparatus according to the present invention, such as
shown generally, e.g., in FIG. 11 or FIG. 15. FIG. 19A details the
stop 73A used with a projection apparatus shown generally in FIG.
11 employing the FIG. 18 RSLM embodiment (when using the FIG. 18
RSLM, the stop 73A replaces the stop 53 in FIG. 11). The stop 73A
is configured similarly to the stop 53 (FIG. 14), except that the
stop 73A defines six exit-side apertures 73Ab, which are
symmetrical around the position x, rather than four exit-side
apertures shown in FIG. 14. The six exit-side apertures 73Ab in
FIG. 19A correspond to the six facets B of the pyramids in FIG. 18,
whereas the four apertures 53b correspond to the four facets of
each pyramid in FIG. 12. Only a single incident-side aperture 73Aa
is required in the stop 73A (FIG. 19a) as in the stop 53 (FIG.
14).
Whenever the FIG. 18 embodiment of an RSLM is employed with a
projection apparatus as shown generally in FIG. 15, a stop 73B is
used as detailed in FIG. 19B. The stop 73B is configured similarly
to the stop 63 (FIG. 16), except that the stop 73B defines six
exit-side apertures 73Bb, which are symmetric around the
incident-side aperture 73Ba, rather than four exit-side apertures
shown in FIG. 16.
FIG. 20 depicts yet another example embodiment of an RSLM according
to the present invention, in which the reflective surface 85a
comprises multiple three-sided pyramids collectively comprising a
microfaceted reflective array. The pyramids are both concave and
convex alternately arranged, wherein T denotes a convex apex and B
denotes a concave apex.
The FIG. 20 embodiment of an RSLM can be employed in a projection
apparatus according to the present invention as depicted generally
in, e.g., FIG. 11 or FIG. 15. FIG. 21A details a stop 83A used with
a projection apparatus shown generally in FIG. 11 employing the
RSLM of FIG. 20 (when using the FIG. 20 RSLM, the stop 83A replaces
the stop 53 in FIG. 11). The stop 83A is configured similarly to
the stop 53 (FIG. 14), except that the stop 8A defines three
exit-side apertures 83Ab, which are symmetrical around the position
x, rather than four exit-side apertures shown in FIG. 14. (The
three apertures 83Ab correspond to the three facets of each pyramid
shown in FIG. 20.) Only a single incident-side aperture 83Aa is
required in the stop 83A.
Whenever the FIG. 20 embodiment of an RSLM is employed with a
projection apparatus as shown generally in FIG. 15, a stop 83B is
used, as detailed in FIG. 21B. The stop 83B is configured similarly
to the stop 63 (FIG. 16), except that the stop 83B defines three
exit-side apertures 83Bb, which are symmetrical around the
incident-side aperture 83Ba, rather than four exit-side apertures
shown in FIG. 16.
FIG. 22 depicts yet another example embodiment of an RSLM according
to the present invention, in which the reflective surface 95a
comprises multiple, alternately disposed parallel ridges T and
valleys B collectively comprising a microfaceted reflective
array.
The FIG. 22 embodiment of an RSLM can be employed in a projection
apparatus according to the present invention as depicted generally
in, e.g., FIG. 11 or FIG. 15. FIG. 23A details a stop 93A used with
a projection apparatus shown generally in FIG. 11 employing the
RSLM of FIG. 22 (when the FIG. 22 RSLM is used, the stop 93A
replaces the stop 53 in FIG. 11). The stop 93A is configured
similarly to the stop 53 (FIG. 14), except that the stop 93A
defines two exit-sided apertures 93Ab, which are symmetrical around
the position x, rather than four exit-side apertures shown in FIG.
14. (The two apertures 93Ab correspond to the two longitudinal
facets defined by each valley and ridge shown in FIG. 20.) only a
single incident-side aperture 93Aa is required in the stop 93A.
Whenever the FIG. 22 embodiment of an RSLM is employed with a
projection apparatus as shown generally in FIG. 15, a stop 93B is
used, as detailed in FIG. 23B. The stop 93B is configured similarly
to the stop 63 (FIG. 16), except that the stop 93B defines two
exit-side apertures 93Bb, which are symmetrical around the
incident-side aperture 93Ba, rather than four exit-side apertures
shown in FIG. 16.
FIG. 24 depicts yet another example embodiment of an RSLM according
to the present invention, in which the reflective surface 105a
comprises multiple convex cones, or alternately concave cones, that
collectively comprise a microfaceted reflective array. T denotes an
apex (convex or concave, respectively) of a cone. Although a cone
is not a planar facet, the conical surface is still functionally
regarded as a facet herein.
The FIG. 24 embodiment of an RSLM can be employed in a projection
apparatus according to the present invention depicted generally in,
e.g., FIG. 11 or FIG. 15. FIG. 25A details a stop 103A used with a
projection apparatus as shown generally in FIG. 11, employing the
RSLM of FIG. 24 (when the FIG. 24 RSLM is used, the stop 103A
replaces the stop 53 in FIG. 11). The stop 103A is configured
similarly to the stop 53 (FIG. 14), except that the stop 103A
defines an annular exit-side aperture 103Ab, which is symmetrical
around the position x, rather than four exit-side apertures shown
in FIG. 14. (The annular aperture 103Ab corresponds to the conical
"facets" shown in FIG. 24.) As in FIG. 14, the stop 103A has a
single incident-side aperture 103Aa.
Whenever the FIG. 24 embodiment of an RSLM is employed with a
projection apparatus as shown generally in FIG. 15, a stop 103B is
used, as detailed in FIG. 25B. The stop 103B is configured
similarly to the stop 63 (FIG. 16), except that the stop 103B
defines an annular exit-side aperture 103Bb, which is symmetrical
around the incident-side aperture 103Ba, rather than four exit-side
apertures shown in FIG. 16.
In FIGS. 25A and 25B support members 103Ac, 103Bc, respectively,
are used to support the central light shielding areas 104, 105 in
the exit-side apertures 103Ab, 103Bb, respectively. However, the
support members 103Ac, 103Bc, respectively, are not necessary if
the stops 103A, 103B, respectively, are constructed so that the
light shielding area 104, 105 is formed on a transparent material
spanning the exit-side aperture 103Ab, 103Bb, respectively, having
a thickness that will not impart any undesired optical aberration
or other image-degrading effect.
In a projection apparatus according to FIG. 11 employing an RSLM
according to FIG. 12, 17, 18, 20, or 22, wherein the illumination
optical system and the projection optical system are not coaxial
with respect to each other, it is necessary to accurately align the
stop relative to the light axis Z. It is also necessary in such an
apparatus to accurately align the RSLM with respect to the light
axis Z and the stop.
In a projection apparatus according to FIG. 15 employing an RSLM
according to FIG. 12, 17, 18, 20, or 22, wherein the illumination
optical system and the projection optical system are coaxial, the
stop can have any of various orientations relative to the light
axis Z. However, it is necessary to accurately align the
orientation of the stop with the orientation of the RSLM.
In a projection apparatus according to FIG. 11 employing an RSLM
according to FIG. 24, wherein the illumination optical system and
the projection optical system are not coaxial, it is necessary to
accurately align the stop 103A relative to the light axis Z.
However, the RSLM 105 can have any of various orientations.
In a projection apparatus according to FIG. 15 employing an RSLM
according to FIG. 24, wherein the illumination optical system and
the projection optical system are coaxial, the stop 103B can have
any of various orientations relative to the light axis Z. Also, the
RSLM 105 can have any of various orientations, which is very
convenient.
The light source in a projection apparatus according to the present
invention is not limited to light sources that produce a
substantially parallel light flux, as were used in the example
implementations described above. Any of various divergent types of
the light sources can be satisfactorily employed by modifying the
conjugate relationship of the light source with the surface being
illuminated. Also, the configuration of the light source is not
limited to the reflector type indicated in the figures. Other types
can satisfactorily be used, and rod or fly-eye lenses can also be
used in the illumination optical system to improve irradiance
uniformity.
According to this invention, as described above, image-contrast
degradation due to ghost light from the surface of an RSLM can be
prevented in a projection apparatus employing an RSLM. Furthermore,
the construction of the projection apparatus can be simplified
compared to prior-art apparatus.
The various embodiments described herein are intended, in any case,
to clarify the technical content of this invention. This invention
should not be narrowly interpreted as being limited to these
embodiments; this invention encompasses any of various
modifications falling within the spirit of the invention and within
the scope of the following claims.
* * * * *